Actually, it is rumoured amoung Quadraphonic fans that Capitol had intentions to release Quadraphonic releases of Abbey Road, Get Back, and Hey Jude in the hey day early 70's. The Capitol execs where the only ones who didn't jump on the fad and most of the projects to be remixed in Q8, Open Reel, or Quad SQ LP where scrapped. Overseas and in Japan they did release a few that made the retail market, but those sold so few and are so hard to confirm existence, most Quadraphiles don't have a clue they are even availible.
It is very possible some Beatles material was released in some type of Multi-Channel format, however I am not certain the public would be receptive or even care about multi-channel releases right now. Alternate Stereo mixes on one CD, or as mention previously Stereo/Mono, and a few good alternate demos would be the way to go with Beatles material.
As a Multi-Channel fan, I personally would have to think about purchasing 5.1 Beatles and the value and enjoyment I would get from a multi-channel mix created 30 years after the fact and most likely by and engineer who has no clue what mixing the format is all about.